KA3: membrane proteins: movement of molecules across membranes

Question 1

describe the fluid mosaic model of the cell membrane

Answer 1

-describes the structure of the plasma membrane

-comprised of a bilayer of phospholipids molecules and a patchwork of protein molecules

-phospholipids are constantly changing position, giving the membrane its fluid quality

-cholesterol may be found within the membrane, acting to reduce membrane fluidity, it also prevents the membrane from solidifying at low temps

Question 2

what do regions of hydrophobic R groups allow?

Answer 2

Strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer

Question 3

describe the head region of the phospholipid bilayer

Answer 3

hydrophilic (attracted to water)

Question 4

Describe the tail region of a phospholipid.

Answer 4

• made up of the fatty acids (uncharged and non-polar)
• hydrophobic (repelled by water)

Question 5

some integral membrane proteins are…

Answer 5

transmembrane proteins

Question 6

Describe integral proteins

Answer 6

-held firmly in place within the membrane

-interact extensively with the hydrophobic region of membrane phospholipids

Question 7

describe peripheral proteins

Answer 7

-have hydrophilic R groups on their surface

-bound to the surface of membranes by ionic and hydrogen bond interactions

-interact with the surfaces of integral membrane proteins

Question 8

What is the phospholipid bilayer?

Answer 8

a barrier to ions and most uncharged polar molecules

Question 9

give examples of molecules which pass through the bilayer by simple diffusion

Answer 9

oxygen and carbon dioxide

Question 10

Describe facilitated diffusion

Answer 10

the passive transport of substances across the membrane through specific transmembrane proteins.

Question 11

how do cells perform specialised functions?

Answer 11

different cell types have different channel and transporter proteins.

Question 12

what are most channel proteins in animal and plant cells?

Answer 12

highly selective

Question 13

what are channels?

Answer 13

multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane

Question 14

what can channel proteins be and what is this effect?

Answer 14

-gated

-change conformation to allow or prevent diffusion

Question 15

how does water cross the membrane?

Answer 15

diffusion through the lipid bilayer and through water channels called aquaporins

Question 16

what are ligand-gated channels controlled by?

Answer 16

binding of signal molecules

Question 17

what are voltage-gated channels controlled by?

Answer 17

changes in ions concentrations

Question 18

what is the role of a transporter protein?

Answer 18

bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane

Question 19

why do transporters alternate between two conformations?

Answer 19

so that the binding site for a solute is sequentially exposed on one side of the bilayer, to the other

Question 20

describe the process of active transport

Answer 20

-uses pump proteins that transfer substances across the membrane against their concentration gradient

Question 21

what are pumps that mediate active transport?

Answer 21

transporter proteins coupled to an energy source

Question 22

give an example of active transport

Answer 22

sodium potassium pump

Question 23

what is required for active transport?

Answer 23

a source of metabolic energy

Question 24

why do some active transport proteins hydrolyse ATP?

Answer 24

to provide the energy for the conformational change required to move substances across the membrane

Question 25

describe the role of ATPases

Answer 25

hydrolyse ATP